Production of alkyl aluminum hydrides and their complex compounds with alkali hydrides



PRODUCTION OF ALKYL ALUMINUM HYDRIDES AND THEIR COMPLEX COMPOUNDS WITHALKALI HY DRIDES Karl Ziegler, Hans-Georg Gellert, and Konrad Nagel,Mulheim an der Ruhr, Germany; said Gellert and Nagel assignors to KarlZiegler, Mulheim an der Ruhr, Germany No Drawing. Application April 8,1953 Serial No. 347,604

Claims priority, application Germany April 21, 1952 14 Claims. (Cl.260448)' This invention relates to the production of alkyl aluminiumhydrides and their complex compounds with alkali hydrides.

O. Stecher and E. Wiberg have described mixed aluminium hydride methylcompounds in Berichte der Deutschen Chemischen Gesellschaft, vol. 75,pp. 2003- 2012 (1942). The process for their preparation consisted inthe action of high-frequency electric discharges on mixtures ofaluminium trimethyl vapour with hydrogen. This process is not veryconvenient; moreover it yields a plurality of different products and isout of the question for the technical production of such compounds.

More recently R. S. Brokaw and R. N. Pease have stated in the Journal ofthe American Chemical Society, 72, p. 3237 (1950), that they obtaineddiethyl aluminium hydride from aluminium boron hydride and ethylene.This process would be out of the question for the technical productionof diethyl aluminium hydride even if, which is not the case, it reallyled to diethyl aluminium hydride. The properties of pure diethylaluminium hydride were established for the first time in the course ofthe development of the present invention. They are quite different fromthose given by the American authors. The latter must, therefore, havehad something else in their hands.

It has now been found that organic aluminium compounds of the generalformula AlHXY, in which X represents an alkyl, R, and Y representshydrogen or an alkyl R, and their complex compounds with alkalihydrides, can be produced by reacting alkyl aluminium dihalides ordialkyl aluminium monohalides with alkali hydrides.

If alkali hydrides, for example sodium hydride, are reacted with dialkylaluminium halides, for example dialkyl aluminium chloride, dialkylaluminium hydrides are obtained together with sodium chloride. Alkylaluminium dihydrides are obtained by the action of alkali hydrides, forexample lithium hydride, on alkyl aluminium dihalides, for example alkylaluminium dichloride.

These reactions are illustrated by the following equations:

The compounds have similar properties in many respects to aluminiumhydride, but are distinguished by greater stability. The stability isparticularly pronounced in the case of dialkyl aluminium hydrides. Theseare readily mobile liquids which are colourless, spontaneouslyinflammable when of low molecular weight, sensitive to air and moistureand distillable in vacuum or high vacuum, and are very similar inappearance to the aluminium trialkyls. Only dimethyl aluminium hydrideis highly viscous. The dialkyl aluminium hydrides do not form stablemolecular compounds with ethers.

United States Patent 0 2,915,541 Patented Dec. 1, 1959 2 The alkylaluminium hydrides are best prepared and kept only in solution, since onconcentration they tend to disproportion in accordance with the equationThe stability, however, depends to a high degree on the absence orpresence of traces of catalytically active impurities which have so farnot been clearly recognised. As a rule the aluminium dialkyl hydrides inthe pure form are stable at least up to C. and to a higher temperaturewhen in solution.

All compounds of the type R AlH and RAlH can add on one molecule ofalkali hydride to form complex compounds of the type (R AlH )Na(Li) or(RAlH )Na(Li) respectively. To prepare the latter substances alkalihydride is advantageously brought together in excess with dialkylaluminium halides or alkyl aluminium dihalides, whereupon the followingreactions take place:

R AlCl+2LiH= (R AlH Li +LiCl RAlCl +3LiH= (RAH-I Li +LiCl From thesecomplex compounds, which are frequently readily soluble in indifferentmedia, the non-complex basic compounds can be recovered by the action ofR AlCl or RAlCl; (thus by a process involving two stages in all):

As compared to the direct reaction of alkali hydride with alkylatedaluminum halide this process has the advantage that it is not necessaryin the first phase of the reaction to employ exactly equivalentquantities of the reactants. The difiiculties of such a one-stagereaction are obvious: If the reaction is not quite complete the reactionproduct still contains halogen. If the reaction mixture is boiled for along time to complete the reaction, this promotes in certaincircumstances the decomposition of the mixed alkyl hydride alreadyformed. If on the other hand the hydride is present in slight excess itis indeed easy to obtain halogen-free reaction products. As aconsequence, however, non-volatile alkali hydride complex compoundsremain behind on vacuum distillation with consequent reduction in yield.All these disadvantages are avoided by the two-stage process. In thatcase one can use only a small excess of alkali hydride, then determinethe alkali content by titration of a sample of the liquid reactionmixture, which has preferably been clarified by centrifuging and hasbeen decomposed with water, and then again add the exactly equivalentquantity of alkyl aluminium halide. It may also be advantageous to beginwith the final alkyl aluminium hydrogen compounds, add alkali hydride tothese and in this way first convert the alkali hydride into a bettersoluble form and then add the alkyl aluminium halogen compound in aquantity corresponding to the alkali. By the repetition of theseoperations large quantities of the hydride and halide are finallyreacted.

The products of the process are excellent reducing agents which in manycases are more effective than the known lithium aluminium hydride, moreparticularly since they can be used at elevated temperature also. Theyare very suitable for the reduction or the partial I PM" t... a (A J2,915,641 3 4 reduction of olefins or diolefins by the process describedIf the addition of the second portion of dipropyl aluin German patentapplication Z 1955 IVc/l2o. Finally minium chloride is omittedandunstead the ethereal sothese aluminium compounds, which contain hydrogenlution freed from lithium CiliOIldBdS evaporated under as well as alkyl,offera convenient transition to alumininitrogen, then a white salt-likeresidue of the complex um trialkyls from the aluminium compounds of thetype compound L1AlI-I (C H remains behind in practically AlR Cl andAlRCl which contain alkyl as well as haloquantltatlve y f gen and arereadily accessible from metallic aluminium The aluminium d p p chlorldeq q f th1 S and akyl halides. Whereas, for example (C H AlCl experiment5 p ra y p p d f m m ium icould hitherto only be converted intoaluminium tri- P PY y addltloll 0f a1uIT 11I}1um Qhlorlde 111 the ethylby treatment with metallic sodium according to the molecular ratio 2:1.The aluminium tripropyl can be equation obtained inter alia from lithiumaluminium hydride and 3-6 mols of propylene at 100 C. in the autoclave,by l 3 (C2H5)2A1c1+3:}fa A1+?(c2H5)3Al blowing off the excess propylene,dissolving or suspending with loss of bound aluminium, whilst thisprocess also in hexane the lithium aluminium dipropyl produced and gavea poor yield, the reaction adding /3 mol of aluminium chloride.Aluminium dihexyl hydride (C H AlH was also obtained in analog- H l 1 613 2 A1(C2 5)2C +NaH A (C2H5)2H+NaCl ous manner. The product passes overat 120 C. in an z 5)2 2 4= 2 5)3 apparatus for short-path distillationunder very high vacucan be carried out very smoothly. The products ofthe um and has the correct analyucal composmon' process of the inventionare also excellent polymerisation Example 3 promoters for ethylene andits homologues by the process g. of sodium hydride are finely ground,suspended of German Patent apphcanon Z 771 Ive/39c in 100 cc. of octaneand added to 120 g. of aluminium Example 1 diethyl chloride containingno solvent, thereupon the A very fine and uniform suspension of 82 g. oflithium 25 mixture is heated with stirring under nitrogen until ahydride in 150 of absclute dig/thy! ether is first sample of the clearsolution, withdrawn after allowing duced by grinding under ether in aball mill or vibrating the,mlxture Settle no longer mmakns halogen Theball mill for a considerable time. 120 g. of aluminium Sodium chlonde iq q Separates well m.coarsdy granu' diethyl chloride are dissolved in200 cc. of absolute i hquld lsfinered or cenmfiiged from the ether in anatmosphere of nitrogen in a three-necked flask sqdiumyhlonde undermtrogen the octane 1s removed by of one-litre content provided withstirrer, dropping fundistlnanon PF mde rate,1y reduced Pressure and thenel and reflux condenser. The lithium hydride suspendlethyl alummmmhydnde 13 Isolated as m Example sion is then added drop by drop withstirring. After Example 4 boiling up the reaction immediately begins andlithium chloride is precipitated. The reaction mixture is then 50 ofaluminium m-lsobutyl etherate heated for approximately a further /2 hourto gentle 2 a)s- 2 5)2 boiling. If the stirring is now interrupted thelithium e mm Hg water clear liquid) chloride {apidly Separates and asmall Sample of the duced from an ethereal solution of aluminium hydrideclear solutlon can readily be withdrawn. Halogen should 40 by carefulheating with isobutylene to in an :g g i z gfi fitgtfig gs i fs zfiautoclave, evaporation of the ether under nitrogen and necessary alittle more thing! y i g i g glu d stillation in vacuo, are dissolved inan atmosphere of minium chloride must be added A consfier b1 nitrogen in150 cc. of air-free absolute ether and 53 g. tent of alkali at thisstage means a decreas e in thi ii ri zii f arllhydwgs alummlum chloridedlssolved m 200 of 2 yield. lreferably the reaction mixture is nowcentrifuged giggi g 535: zgi i gif igg gg 31:21:12: 2} 333 L: 233 3 igifg gzifg ig P fine suspension of 10 g. of lithium hydride stirred underatmos hgere of nitro en The f S 5 an n trogen, whereupon with prec ptation of lithium ch10 gently as possible on a hot water bath snd ih eresidue i i g i g g fi lsobuigyl trihydr-ide I 1 z 4 9 is orme w ic cane recognised 2 2F 3 52 232 E i: 3 g' g g g g gg by the fact that theethereal solution, previously clarified g p g' f water c1ear regdil d bysettl ng, now conta ns the correct quantity of alkali a mximatel 60 70 A5 Y e 1 in solution. If the lithium chloride is now separated by fggndas calgulatezl di 0 ga i g i fig gk amt? centrifuging (in closedcentrifuge vessels filled with nitro- 4 D gen), a clear solution isobtained to which the unused gg s gfig ii fi g f a gs i f :l g on 55 /aof the isobutyl aluminium dichloride solution is now of as g i'g 290 0 Estamedgave added. After again separating the lithium chloride which a uth h W conslste again precipitates a clear solution of isobutylaluminium c y 0 3 e ane an 3 y dihydride is obtained which can becautiously concen- E l 2 ti'ated but finally deposits solid insolublealuminium hydride. Samples of the concentrated but not yet turbid15.oflthu hd are bo iled iii 2 5O cc. of t h r i ri fl ib fip p a r tiis z cfib d solutionglve hydrogen and {so-butane m the quanmatwe inExample 1 with 74 g. of dipropyl aluminium chloride propomon 2:1 ondecomposmon with water with stirring. Lithium chloride againprecipitates and Example 5 the complex salt LiA1H2(C3H7)2 goes intosolution r Di-propyl aluminium chloride (preparation, see Exg i 2 s fffig i m fh on 1 f i l fi ample 2) is heated in hexane in an autoclaveunder an stanc iing quietly increz es i o agprfxi rii t el; 2 h l aiiiii g i of igg li i) g 3 mols of sodium hydride or ours to After coolingand settling then remains constant. The solution is clarified a ain bycentrifuging, the clear solution is separated ur ider g iz flii i h232512 i ggl ff gifii i -i i g gi nitrogen and 74 of dipropyl aluminiumchloride are clave is transferred With the same care to i he s'ime fiasiagain addfid- The last Portions are added cautiously the material isheated to bo li n and the h xane solutiori and the solution isfrequently tested for halogen or alkali. is separated while hot.Sodiurii aluminium dipropyl dig e woiklmg1 up Is s milar to Example 1.The aluminium hyride in the form of beautiful colourless crystals is obipiopy 1y iide boils under very high vacuum at 8v C. 75 tamed on coolingand completely on evaporation (in an atmosphere of nitrogen). Thecomplex sodium aluminium compound is finally obtained in almostquantitative yield by exhaustive extraction with hot hexane of the massof salt which originally remained undissolved. The salt contains16.616.8% of sodium, 19.419.8% of aluminium (theoretical quantities:16.7% and 19.5% respectively) and on decomposition with water gives agas which consists of hydrogen and propane in exactly equal proportions.

What we claim is:

1. Process for the production of organic aluminium compounds of thegeneral formula AlHXY, in which X is an alkyl radical and Y is a memberselected from the group consisting of alkyl radicals and hydrogen, andtheir complex compounds with alkali metal hydrides, which comprisesreacting an alkyl aluminium halide with at least one mol of about amolar excess of alkali metal hydride per halogen atom of said halide.

2. As a new chemical compound, an unadulterated specific organicaluminum compound of the general formula All-IXY, in which X and Y arealkyl radicals containing at least 2 carbon atoms.

3. As a new chemical compound, an unadulterated specificdiethylaluminumhydride.

4. As a new chemical compound, an unadulterated specificdipropylaluminumhydride.

5. As a new chemical compound, an unadulterated specificisobutylaluminumdihydride.

6. As a new chemical compound, an unadulterated specificdihexylaluminumhydride.

7. Process for the production of alkyl aluminum hydrides which comprisesreacting an alkyl aluminum halide with a suflicient amount of an alkalimetal hydride to provide at least about one mol of said hydiide for eachhalogen of said halide plus about one mol of said hydride to therebyobtain an alkali metal alkyl aluminum hydride, and thereafter reactingthe latter with sufiicient .6 alkyl alminum halide to provide for eachalkali metal present in said alkali metal alkyl aluminum hydride substantially molar equivalent amounts of halogen.

8. Process according to claim 7, in which said alkyl aluminum halide isa monoalkyl aluminum dihalide.

9. Process according to claim 8, in which said dihalide is one having alower alkyl radical of at least two carbon atoms.

10. Process according to claim 7, in which said alkyl aluminum halide isa dialkyl aluminum monohalide.

11. Process according to claim 10, in which said mono halide is onehaving lower alkyl radicals with at least two carbon atoms each.

12. In the production of alkyl aluminum hydrides, the improvement whichcomprises reacting an alkali metal alkyl aluminum hydride withsufficient alkyl aluminum halide to provide for each alkali metalpresent in said hydride substantially molar equivalent amounts ofhalogen and recovering the alkyl aluminum hydride formed.

13. Process in accordance with claim 7, in which said halide is reactedwith said hydride at a temperature up to about C. in the substantialabsence of a solvent.

14. Process in accordance with claim 7, in which said halide is reactedwith said hydride at a temperature above about 120 C. in the presence ofan inert solvent.

Grosse et al.: J. Am. Chem, vol. 5, page 110. Grosse et al.: J. OrganicChemistry (1940), page 107. Finholt et al.: J. Sm. Chem. Soc., vol. 69,page 1199.

1. PROCESS FOR THE PRODUCTION OF ORGANIC ALUMINIUM COMPOUNDS OF THEGENERAL FORMULA AIHXY, IN WHICH X IS AN ALKYL RADICAL AND Y IS A MEMBERSELECTED FROM THE GROUP CONSISTING OF ALKYL RADICALS AND HYDROGEN, ANDTHEIR COMPLEX COMPOUNDS WITH ALKALI METAL HYDRIDES, WHICH COMPRISESREACTING AN ALKYL ALUMINIUM HALIDE WITH AT LEAST ONE MOL OF ABOUT AMOLAR EXCESS OF ALKALI METAL HYDRIDE PER HALOGEN ATOM OF SAID HALIDE.